This research is designed to investigate nutritionally-induced alterations in hormones and the energy needs of the body. It is specifically designed to study the effects of over- and undernutrition on thyroid hormone and catecholamine metabolism, and the possible effects these changes have on thermogenesis and the body economy. Nutritionally-induced changes in the metabolism of thyroid hormones and catecholamines will be correlated with changes in thermogenesis to determine whether these changes represent adaptive responses with important survival value.